Structural, theoretical and spectroscopic studies of the dichloride hexahydrate cube [Cl2(H2O)6]2−

Abstract

The structure of the dichloride hexahydrate cube, [Cl₂(H₂O)₆]²⁻, as a salt with the tris(diisopropylamino)cyclopropenium cation, [C₃(NⁱPr₂)₃]⁺, has been determined by low-temperature X-ray and neutron-diffraction studies. H atoms not involved in O–H⋯Cl bonding are disordered over two 0.5 occupancy sites around the O₆ ring. Calculations of the dianionic cube in the gas phase show remarkably good agreement with the solid-state structures with the exception of short O–H bond distances around the O₆ ring that suggests the involvement of a dynamic process. The cluster was also characterised by single-crystal infrared spectroscopy, and vibrational wavenumbers were found to be in good agreement with hydrogen bonding distances. Dibromide and difluoride hexahydrates were also studied theoretically, and O⋯O distances were found to decrease in the order difluoride > dichloride > dibromide > (H₂O)₆ and as O⋯O⋯O angles increased towards an almost planar ring in (H₂O)₆. NMR spectra of a chloroform solution of the hydrated salt at −25 °C is consistent with cluster formation.